Therapeutic modification of blood viscosity has an important role to play in the management of Chronic Occlusive Arterial Disease (COAD). Various treatments including hemodilution and drugs have been proposed and used to accomplish this end. However, measurements of fresh whole blood viscosity (FWBV) are rarely used in the diagnosis or management of COAD due to lack of suitable instrumentation. This study is designed to evaluate the utility of FWBV in the diagnosis and treatment of COAD. The viscosity measurements will be made with a new clinical whole blood viscometer we have developed which generates a blood viscosity profile (i.e. relation between viscosity and shear rate). Also, a number of parameters sensitive to blood viscosity determinants such as hematocrit and red blood cell deformability are calculated from the profile. For this study we will use a suitable clinical model of COAD, namely patients with symptoms of intermittent claudication of the legs. It is a disorder which is well defined, easily diagnosed and evaluated over time. It is also an early indicator of more serious arterial dysfunction which often follows. We will study the usefulness of blood viscosity measurements in this condition with several patient groups receiving placebo, no treatment, or pentoxifylline, a drug known to increase red blood cell deformability and hence reduce viscosity. Suitable control groups consisting of at risk but asymptomatic patients, age-matched asymptomatic patients not at risk, and healthy younger controls will be studied. The results should provide the basis for evaluating FWBV measures as a clinically useful tool in COAD.